Many cells in the human body possess a singular projection from their surface called a primary cilium. Although the existence of primary cilia has been recognized for over a century, only recently has it become clear that they function in the detection and interpretation of important intercellular cues. Some of these cues, such as Hedgehog signals, are key regulators of embryonic patterning and adult tissue homeostasis. Consequently, defects in Hedgehog signaling can cause birth defects and some forms of cancer. Similarly, defects in primary cilia can cause rare congenital syndromes such as Meckel and Joubert syndromes, may underlie more common human diseases such as polycystic kidney disease, and are important for the progression of some cancers. Mammalian cells with ciliary defects fail to respond to Hedgehog signals. We have found that some tissues are ciliated at specific times in development, and within adult tissues, some cells can be ciliated and others not. We hypothesize that the control of which cells are ciliated shapes how tissues respond to cilium-interpreted signals. We have recently identified a class of novel genes called the Tectonics, which support ciliogenesis in some tissues and control ciliary membrane composition in others. The Tectonics interact and co-localize with ciliary disease proteins at a subdomain of the cilium called the transition zone. We propose to study Tectonics and their interactors to understand the tissue-specific regulation of ciliary functions. Specifically, we will answer three complementary questions: 1) Do different Tectonics regulate ciliogenesis in different tissues? 2) Do Tectonics and other transition zone components promote ciliogenesis by regulating protein transport to the cilium? 3) Do Tectonics function with human disease genes, such as those underlying Meckel syndrome and polycystic kidney disease, to regulate ciliogenesis? The proposed experiments combine genetic, imaging and biochemical approaches to provide answers to these questions. This work will elucidate the mechanism by which Tectonics and associated proteins contribute to ciliary function, providing molecular and cell biological insights into how cilia function in development and how they misfunction in human ciliopathies.